1. Field of the Invention
Methods consistent with the present invention relate to routing, and more particularly, to routing which establishes a data transfer path from a source node to a destination node in a wireless personal network such as a Zigbee network.
2. Description of the Related Art
A personal area network (PAN), as contrasted with a local area network (LAN) or a wide area network (WAN), enables each individual to have a unique network of his own. That is, devices owned by individuals each constitute one network for the purpose of their convenience. As an effort to achieve such a PAN implemented in a wireless manner, the IEEE 802.15 Working Group defines the Wireless Personal Area Network (WPAN) as the short-range wireless network standards, and has four Task Groups (TG) thereunder.
IEEE 802.15.1 defines the well-known Bluetooth technology standards, and IEEE 802.15.3 and IEEE 802.15.3a define the high-rate WPAN standards. IEEE 802.15.4, called “Zigbee”, defines the low-rate WPAN standards, the data rate of which is no more than 250 Kbps.
One of the important tasks of the Zigbee Network Group is to define a efficient routing method for a wireless sensor network. An On-Demand routing method, such as Ad hoc On Demand Distance Vector (AODV) routing, can establish an efficient path in an Ad hoc-type wireless network, but such a routing method requires each node to have a routing table in order for the node to forward data packets. However, most wireless sensors have a limited amount of memory space, so there exist difficulties in building the routing table in the memory space.
Meanwhile, a tree routing method can solve such a memory-limitation problem. However, the tree routing method based on the tree structure is not efficient, in one aspect, in establishing a path, so the routing method for the Zigbee wireless network has not been standardized up to now.
FIG. 1 is a view for explaining a conventional routing method based on the tree routing. In FIG. 1, a node E indicates a source node (src) and a node I indicates a destination node (dest). Further, the sign “+” is marked on nodes having a routing table, the sign “−” is marked on nodes having no routing table, and the same signs are marked in the remaining drawings.
In FIG. 1, the source node E forwards data to a node B which is a parent node of the node E. The node B buffers the data received from the node E, broadcasts a route request (RREQ) packet, and searches for a path. The RREQ packet is repeatedly broadcast to a node D so that the path is searched for. The node D is aware that the destination node I is its child node, and unicasts the RREQ packet to the node I. The node I responds to the unicast RREQ packet with a route reply (RREP) packet. The node B receives the RREP packet, stores a searched path in the routing table, and forwards buffered data.
However, as shown in FIG. 1, in the situation that the node B forwards data to a node N, the routing method used in the wireless network, such as a Zigbee network, searches for a path, as aforementioned, even when the node B is aware of information on paths to the node I. Likewise, a node G, which is a child node of the node C, searches for a path in the same way as above even when forwarding data to the node N.
That is, even when there has been the previously searched path to the parent node I of the node N, the routing method as above looks for a path without considering the searched path. Accordingly, the routing method repeats unnecessary broadcasts for a path even though the previously searched path is available, which increases the overhead on a network to delay the entire data delivery.